Hybrid circuits are commonly fabricated by thick film techniques in semiconductor integrated circuit technology. Thick film is often used because it is relatively economical, easy to process and requires less capital investment than thin film technologies. Thick film also allowed circuits to be built on multiple layers for higher densities.
Current thick film processing includes screen printing a thick film paste onto a ceramic substrate. The substrate is then dried and fired in order to sinter the paste. Although this technique is sufficient for many applications, current circuit density on multilayered hybrid circuits is restricted by the resolution available through conventional screen printing. Generally, state of the art screen printing line resolution is 0.005 inches, which is not satisfactory for new technologies which will require 0.002 to 0.003 inch resolution. Thin film processes allow high resolution, but are generally limited to single layer circuitry, and are relatively expensive and time consuming.
Lasers have been heretofore proposed for conductor formation in thick film circuits. For example, the article entitled "New Thick Film Multilayer Interconnection Technology Using a Nd-YAG Laser" by Ohsaki et al., 1982, IEEE, defines the use of a laser to heat gold conductor paste to form gold conductors in a thick film circuit. However, a need has arisen for a technique to form and pattern very thin copper conductors in thick film integrated circuits, as copper is much less expensive than gold and permits better rework with solder.